Enhanced handover procedures in communication network environment

Abstract

Techniques are disclosed for enhanced handover operations in a communication network environment. For example, from a user equipment perspective, a method includes receiving, at the user equipment, a radio resource control message from a radio access node with which the user equipment is connected, the radio resource control message including handover-enabling data to enable the user equipment to perform multiple handover operations in response to the radio resource control message, and utilizing, by the user equipment, the handover-enabling data to perform the multiple handover operations.

Description

[0001] ENHANCED HANDOVER PROCEDURES IN COMMUNICATION NETWORK ENVIRONMENT

[0002] Field

[0003] The field relates generally to communication networks, and more particularly, but not exclusively, to security management in such communication networks.

[0004] Background

[0005] This section introduces aspects that may be helpful in facilitating a better understanding of the inventions. Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art.

[0006] Fourth generation (4G) wireless mobile telecommunications technology, also known as Long Term Evolution (LTE) technology, was designed to provide high-capacity mobile multimedia with high data rates particularly for human interaction. Next generation or fifth generation (5G) technology is intended to be used not only for human interaction, but also for machine type communications in so-called Internet of Things (loT) networks.

[0007] While 5G networks are intended to enable massive loT services (e.g., very large numbers of limited capacity devices) and mission-critical loT services (e.g., requiring high reliability), improvements over legacy mobile communication services are supported in the form of enhanced mobile broadband (eMBB) services providing improved wireless Internet access for mobile devices.

[0008] In an example communication system, user equipment (5G UE in a 5G network or, more broadly, a UE) such as a mobile terminal (subscriber) communicates over an air interface with a base station or access point of an access network referred to as a 5G AN in a 5G network. The access point (e.g., gNB) is illustratively part of an access network of the communication system.

[0009] For example, in a 5G network, the access network referred to as a 5G AN is described in 5G Technical Specification (TS) 23.501, entitled “Technical Specification Group Services and System Aspects; System Architecture for the 5G System,” and TS 23.502, entitled “Technical Specification Group Services and System Aspects; Procedures for the 5G System (5GS),” the disclosures of which are incorporated by reference herein in their entireties. In general, the access point (e.g., gNB) provides access for the UE to a core network (CN or 5GC), which then provides access for the UE to other UEs and / or a data network such as a packet data network (e.g., Internet).

[0010] TS 23.501 goes on to define a 5G Service-Based Architecture (SBA) which models services as network functions (NFs) that communicate with each other using representational state transfer application programming interfaces (Restful APIs).

[0011] Furthermore, TS 33.501, entitled “Technical Specification Group Services and System Aspects; Security Architecture and Procedures for the 5G System,” the disclosure of which is incorporated by reference herein in its entirety, further describes security management details associated with a 5G network.

[0012] Security management is an important consideration in any communication network environment. However, due to continuing attempts to improve the architectures and protocols associated with a 5G network, and / or other networks, in order to increase network efficiency and / or subscriber convenience, security management issues associated with UE mobility between cells in a communication network environment (e.g., handovers) can present a significant technical challenge.

[0013] Summary

[0014] Illustrative embodiments provide techniques for enhanced handover operations in a communication network environment.

[0015] In one illustrative embodiment, from a user equipment perspective, a method includes receiving, at the user equipment, a radio resource control message from a radio access node with which the user equipment is connected, the radio resource control message including handover-enabling data to enable the user equipment to perform multiple handover operations in response to the radio resource control message, and utilizing, by the user equipment, the handover-enabling data to perform the multiple handover operations.

[0016] In another illustrative embodiment, from a radio access node perspective, a method includes generating, at the radio access node, a radio resource control message comprising handover-enabling data to enable user equipment to perform multiple handover operations in response to the radio resource control message, and sending, from the radio access node, the radio resource control message to the user equipment. In some illustrative embodiments, the handover-enabling data includes security configurations to enable the apparatus to perform multiple handover operations in response to the radio resource control message. The security configurations may include key derivation parameters for performing one or more key derivation procedures.

[0017] In some illustrative embodiments, the handover-enabling data includes a master key update information element.

[0018] In some illustrative embodiments, the handover-enabling data includes an intra-radio access node handover key change indicator settable by one or more target radio access nodes. When the intra-radio access node handover key change indicator is set to a first value, the user equipment performs a key change for an intra-radio access node handover for a corresponding target radio access node, and when the intra-radio access node handover key change indicator is set to a second value, the user equipment does not perform a key change for an intra-radio access node handover for a corresponding target radio access node.

[0019] In some illustrative embodiments, the handover-enabling data comprises an indication that the user equipment is not allowed to perform a handover operation until a security update is performed.

[0020] In some illustrative embodiments, the multiple handover operations are lower layer- triggered mobility (LTM) handover operations.

[0021] Advantageously, illustrative embodiments provide enhanced LTM handover procedures that enable user equipment to perform subsequent handovers without a new reconfiguration message (e.g., radio resource control (RRC) reconfiguration message) being sent from a source or target radio access node to the user equipment.

[0022] Further illustrative embodiments are provided in the form of a non-transitory computer readable medium having embodied therein executable program code that when executed by a processor causes the processor to perform the above and / or other steps, operations, and the like. Still further illustrative embodiments comprise an apparatus with a processor and a memory configured to perform the above and / or other steps, operations, and the like. Some illustrative embodiments comprise a system configured to perform the above and / or other steps, operations, and the like. Further, some illustrative embodiments comprise an apparatus or a system comprising means for performing the above and / or other steps, operations, and the like.

[0023] These and other features and advantages of embodiments described herein will become more apparent from the accompanying drawings and the following detailed description. Brief Description of the Drawings

[0024] FIG. 1 illustrates a communication network environment with which one or more illustrative embodiments may be implemented.

[0025] FIG. 2 illustrates user equipment and entities with which one or more illustrative embodiments may be implemented.

[0026] FIG. 3 illustrates a key chaining procedure in a communication network environment.

[0027] FIG. 4 illustrates a handover procedure in a communication network environment.

[0028] FIG. 5 illustrates an enhanced handover procedure in a communication network environment according to an illustrative embodiment.

[0029] FIG. 6 illustrates an enhanced handover procedure in a communication network environment according to another illustrative embodiment.

[0030] FIG. 7 illustrates an enhanced handover procedure in a communication network environment according to yet another illustrative embodiment.

[0031] Detailed Description

[0032] Embodiments will be illustrated herein in conjunction with example communication systems and associated techniques for security management in communication systems. It should be understood, however, that the scope of the claims is not limited to particular types of communication systems and / or processes disclosed. Embodiments can be implemented in a wide variety of other types of communication systems, using alternative processes and operations. For example, although illustrated in the context of wireless cellular systems utilizing the 3rd Generation Partnership Project (3GPP) system elements such as a 3GPP next generation system (5G), the disclosed embodiments can be adapted in a straightforward manner to a variety of other types of communication systems such as 6G communication systems.

[0033] In accordance with illustrative embodiments implemented in a 5G communication system environment, one or more 3GPP technical specifications (TS) and technical reports (TR) may provide further explanation of network elements / functions and / or operations that may interact with parts of the inventive solutions, e.g., the above-referenced 3GPP TS 23.501, TS 23.502, and TS 33.501. Other 3GPP TS / TR documents may provide other details that one of ordinary skill in the art will realize, for example, TS 38.401 entitled, “Technical Specification Group Radio Access Network; NG-RAN; Architecture Description,” TS 38.300 entitled, “Technical Specification Group Radio Access Network; NR; NR and NG-RAN Overall Description; Stage 2,” TS 38.331 entitled, “Technical Specification Group Radio Access Network; NR; Radio Resource Control (RRC) Protocol Specification,” and RP-234036 entitled, “New WID: NR Mobility Enhancements Phase 4,” the disclosures of which are incorporated by reference herein in their entireties. Note that 3GPP TS / TR documents are nonlimiting examples of communication network standards (e.g., specifications, procedures, reports, requirements, recommendations, and the like). However, while well-suited for 5G- related 3GPP standards, embodiments are not necessarily intended to be limited to any particular standards.

[0034] It is to be understood that the term 5G network, and the like (e.g., 5G system, 5G communication system, 5G environment, 5G communication environment etc.), in some illustrative embodiments, may be understood to comprise all or part of an access network and all or part of a core network. However, the term 5G network, and the like, may also occasionally be used interchangeably herein with the term 5GC network, and the like, without any loss of generality, since one of ordinary skill in the art understands any distinctions.

[0035] Prior to describing illustrative embodiments, a general description of certain main components of a 5G network will be described below in the context of FIGS. 1 and 2.

[0036] FIG. 1 shows a communication system 100 within which illustrative embodiments are implemented. It is to be understood that the elements shown in communication system 100 are intended to represent some main functions provided within the system, e.g., control plane functions, user plane functions, etc. As such, the blocks shown in FIG. 1 reference specific elements in 5G networks that provide some of these main functions. However, other network elements may be used to implement some or all of the main functions represented. Also, it is to be understood that not all functions of a 5G network are depicted in FIG. 1. Rather, at least some functions that facilitate an explanation of illustrative embodiments are represented. Subsequent figures may depict some additional elements / functions (i.e., network entities).

[0037] Accordingly, as shown, communication system 100 comprises user equipment (UE) 102 that communicates via an air interface 103 with an access point 104. It is to be understood that UE 102 may use one or more other types of access points (e.g., access functions, networks, etc.) to communicate with the 5GC network other than a gNB. By way of example only, the access point 104 may be any 5G access network (gNB), an untrusted non-3GPP access network that uses an Non-3GPP Interworking Function (N3IWF), a trusted non-3GPP network that uses a Trusted Non-3GPP Gateway Function (TNGF) or wireline access that uses a Wireline Access Gateway Function (W-AGF) or may correspond to a legacy access point (e.g., eNB). Furthermore, access point 104 may be a wireless local area network (WLAN) access point as will be further explained in illustrative embodiments described herein.

[0038] The UE 102 may be a mobile station, and such a mobile station may comprise, by way of example, a mobile telephone, a computer, an loT device, or any other type of communication device. The term “user equipment” as used herein is therefore intended to be construed broadly, so as to encompass a variety of different types of mobile stations, subscriber stations or, more generally, communication devices, including examples such as a combination of a data card inserted in a laptop or other equipment such as a smart phone. Such communication devices are also intended to encompass devices commonly referred to as access terminals.

[0039] In one illustrative embodiment, UE 102 is comprised of a Universal Integrated Circuit Card (UICC) part and a Mobile Equipment (ME) part. The UICC is the user-dependent part of the UE and contains at least one Universal Subscriber Identity Module (USIM) and appropriate application software. The USIM securely stores a permanent subscription identifier and its related key, which are used to uniquely identify and authenticate subscribers to access networks. The ME is the user-independent part of the UE and contains terminal equipment (TE) functions and various mobile termination (MT) functions. Alternative illustrative embodiments may not use UICC-based authentication, e.g., a Non-Public (Private) Network (NPN).

[0040] Note that, in one example, the permanent subscription identifier is an International Mobile Subscriber Identity (IMSI) unique to the UE. In one embodiment, the IMSI is a fixed 15 -digit length and consists of a 3 -digit Mobile Country Code (MCC), a 3 -digit Mobile Network Code (MNC), and a 9-digit Mobile Station Identification Number (MSIN). In a 5G communication system, an IMSI is referred to as a Subscription Permanent Identifier (SUPI). In the case of an IMSI as a SUPI, the MSIN provides the subscriber identity. Thus, only the MSIN portion of the IMSI typically needs to be encrypted. The MNC and MCC portions of the IMSI provide routing information, used by the serving network to route to the correct home network. When the MSIN of a SUPI is encrypted, it is referred to as Subscription Concealed Identifier (SUCI). Another example of a SUPI uses a Network Access Identifier (NAI). NAI is typically used for loT communication. The access point 104 is illustratively part of a radio access network or RAN of the communication system 100. Such a radio access network may comprise, for example, a 5G System having a plurality of base stations. Components of a radio access network may, more generally, be considered “radio access entities.”

[0041] Further, the access point 104 in this illustrative embodiment is operatively coupled to an Access and Mobility Management Function (AMF) 106. In a 5G network, the AMF 106 supports, inter alia, mobility management (MM) and security anchor (SEAF) functions.

[0042] AMF 106 in this illustrative embodiment is operatively coupled to (e.g., uses the services of) other network functions 108. Other network functions 108 may include network functions that can act as service producers (NFp) and / or service consumers (NFc). Note that any network function can be a service producer for one service and a service consumer for another service. Further, when the service being provided includes data, the data-providing NFp is referred to as a data producer, while the data-requesting NFc is referred to as a data consumer. A data producer may also be an NF that generates data by modifying or otherwise processing data produced by another NF. Note that NFs may, more generally, be considered “network entities” whereby a network entity that consumes one or more of data and a service can be considered a “consumer network entity” and a network entity that produces one or more of data and a service can be considered a “producer network entity.”

[0043] Note that a UE, such as UE 102, is typically subscribed to what is referred to as a Home Public Land Mobile Network (HPLMN) in which some or all of the functions 106 and 108 reside. Alternatively the UE, such as UE 102, may receive services from an NPN where these functions may reside. The HPLMN is also referred to as the Home Environment (HE). If the UE is roaming (not in the HPLMN), it is typically connected with a Visited Public Land Mobile Network (VPLMN) also referred to as a visited network, while the network that is currently serving the UE is also referred to as a serving network. In the roaming case, some of the functions 106 and 108 can reside in the VPLMN, in which case, functions in the VPLMN communicate with functions in the HPLMN as needed. However, in a non-roaming scenario, access and mobility management functions 106 and the other network functions 108 reside in the same communication network, i.e., HPLMN. Embodiments described herein, unless otherwise specified, are not necessarily limited by which functions reside in which PLMN (i.e., HPLMN or VPLMN). The access point 104 is also operatively coupled (via one or more of functions 106 and / or 108) to a Session Management Function (SMF) 110, which is operatively coupled to a User Plane Function (UPF) 112. UPF 112 is operatively coupled to a Packet Data Network, e.g., Internet 114. Note that the thicker solid lines in this figure denote a user plane (UP) of the communication network, as compared to the thinner solid lines that denote a control plane (CP) of the communication network. It is to be appreciated that Internet 114 in FIG. 1 may additionally or alternatively represent other network infrastructures including, but not limited to, cloud computing infrastructure and / or edge computing infrastructure. Further typical operations and functions of such network elements are not described here since they are not the focus of the illustrative embodiments and may be found in appropriate 3GPP 5G documentation. Note that functions shown in 106, 108, 110 and 112 are examples of network functions (NFs).

[0044] It is to be appreciated that this particular arrangement of system elements is an example only, and other types and arrangements of additional or alternative elements can be used to implement a communication system in other embodiments. For example, in other embodiments, the communication system 100 may comprise other elements / functions not expressly shown herein.

[0045] Accordingly, the FIG. 1 arrangement is just one example configuration of a wireless cellular system, and numerous alternative configurations of system elements may be used. For example, although only single elements / functions are shown in the FIG. 1 embodiment, this is for simplicity and clarity of description only. A given alternative embodiment may of course include larger numbers of such system elements, as well as additional or alternative elements of a type commonly associated with conventional system implementations.

[0046] It is also to be noted that while FIG. 1 illustrates system elements as singular functional blocks, the various subnetworks that make up the 5G network are partitioned into so-called network slices. Network slices (network partitions) are logical networks that provide specific network capabilities and network characteristics that can support a corresponding service type, optionally using network function virtualization (NFV) on a common physical infrastructure. With NFV, network slices are instantiated as needed for a given service, e.g., eMBB service, massive loT service, and mission-critical loT service. A network slice or function is thus instantiated when an instance of that network slice or function is created. In some embodiments, this involves installing or otherwise running the network slice or function on one or more host devices of the underlying physical infrastructure. UE 102 is configured to access one or more of these services via access point 104.

[0047] FIG. 2 is a block diagram illustrating computing architectures for various participants in methodologies according to illustrative embodiments. More particularly, system 200 is shown comprising user equipment (UE) 202 and a plurality of entities 204-1, . . . . , 204-N. For example, in illustrative embodiments and with reference back to FIG. 1, UE 202 can represent UE 102, while entities 204-1, . . . , 204-N can represent functions 106 and 108 (i.e., network entities such as, but not limited to, AMF), as well as access point 104 (i.e., radio access entity such as, but not limited to, a RAN node or gNB). It is to be appreciated that the UE 202 and entities 204-1, . . . . , 204-N are configured to interact to provide security management and other techniques described herein.

[0048] The user equipment 202 comprises a processor 212 coupled to a memory 216 and interface circuitry 210. The processor 212 of the user equipment 202 includes a security management processing module 214 that may be implemented at least in part in the form of software executed by the processor. The security management processing module 214 performs security management described in conjunction with subsequent figures and otherwise herein. The memory 216 of the user equipment 202 includes a security management storage module 218 that stores data generated or otherwise used during security management operations.

[0049] Each of the entities (individually or collectively referred to herein as 204) comprises a processor 222 (222-1, . . . , 222-N) coupled to a memory 226 (226-1, . . . , 226-N) and interface circuitry 220 (220-1, . . . , 220-N). Each processor 222 of each entity 204 includes a security management processing module 224 (224-1, . . . , 224-N) that may be implemented at least in part in the form of software executed by the processor 222. The security management processing module 224 performs security management operations described in conjunction with subsequent figures and otherwise herein. Each memory 226 of each entity 204 includes a security management storage module 228 (228-1, . . . , 228-N) that stores data generated or otherwise used during security management operations.

[0050] The processors 212 and 222 may comprise, for example, microprocessors such as central processing units (CPUs), application-specific integrated circuits (ASICs), digital signal processors (DSPs) or other types of processing devices, as well as portions or combinations of such elements. The memories 216 and 226 may be used to store one or more software programs that are executed by the respective processors 212 and 222 to implement at least a portion of the functionality described herein. For example, security management operations and other functionality as described in conjunction with subsequent figures and otherwise herein may be implemented in a straightforward manner using software code executed by processors 212 and 222.

[0051] A given one of the memories 216 and 226 may therefore be viewed as an example of what is more generally referred to herein as a computer program product or still more generally as a computer or processor readable (non-transitory or storage) medium that has executable program code embodied therein. Other examples of computer or processor readable media may include disks or other types of magnetic or optical media, in any combination. Illustrative embodiments can include articles of manufacture comprising such computer program products or other computer or processor readable media.

[0052] Further, the memories 216 and 226 may more particularly comprise, for example, electronic random- access memory (RAM) such as static RAM (SRAM), dynamic RAM (DRAM) or other types of volatile or non-volatile electronic memory. The latter may include, for example, non-volatile memories such as flash memory, magnetic RAM (MRAM), phasechange RAM (PC-RAM) or ferroelectric RAM (FRAM). The term “memory” as used herein is intended to be broadly construed, and may additionally or alternatively encompass, for example, a read-only memory (ROM), a disk-based memory, or other type of storage device, as well as portions or combinations of such devices.

[0053] The interface circuitries 210 and 220 illustratively comprise transceivers or other communication hardware or firmware that allows the associated system elements to communicate with one another in the manner described herein.

[0054] It is apparent from FIG. 2 that user equipment 202 and plurality of entities 204 are configured for communication with each other as security management participants via their respective interface circuitries 210 and 220. This communication involves each participant sending data to and / or receiving data from one or more of the other participants. The term “data” as used herein is intended to be construed broadly, so as to encompass any type of information that may be sent between participants including, but not limited to, identity data, key pairs, key indicators, tokens, secrets, security management messages, registration request / response messages and data, request / response messages, authorization and / or authentication request / response messages and data, metadata, control data, audio, video, multimedia, consent data, other messages, etc.

[0055] It is to be appreciated that the particular arrangement of components shown in FIG. 2 is an example only, and numerous alternative configurations may be used in other embodiments. For example, any given network element / function and / or access point can be configured to incorporate additional or alternative components and to support other communication protocols.

[0056] Other system elements such as access point 104, SMF 110, and UPF 112 may each be configured to include components such as a processor, memory and network interface. Also, entities such as third-party applications and network operators can participate in methodologies described herein via computing devices configured to include components such as a processor, memory and network interface. These elements and devices need not be implemented on separate stand-alone processing platforms, but could instead, for example, represent different functional portions of a single common processing platform.

[0057] More generally, FIG. 2 can be considered to represent processing devices configured to provide respective security management functionalities and operatively coupled to one another in a communication system. By way of example only, all or parts of each of UE 202 and the plurality of entities 204 (e.g., processor and memory) can be considered examples of means for performing one or more operations, one or more steps, one or more functions, one or more processes, etc. as described herein.

[0058] As mentioned above, the 3GPP TS 23.501 defines the 5GC network architecture as service-based, e.g., Service-Based Architecture (SBA). It is realized herein that in deploying different NFs, there can be many situations where an NF may need to interact with an entity external to the SBA-based 5GC network (e.g., including the corresponding PLMN(s), e.g., HPLMN and VPLMN). Thus, the term “internal” as used herein illustratively refers to operations and / or communications within the SBA-based 5GC network (e.g., SBA-based interfaces) and the term “external” illustratively refers to operations and / or communications outside the SBA-based 5GC network (non-SBA interfaces).

[0059] Lower layer-triggered mobility (LTM) is a new 5G handover procedure with shorter service interruption times in which a gNB receives a measurement report from a UE, and on the basis of the measurement report, the gNB changes the serving cell (e.g., from a source cell to a target cell) of the UE. In the existing LTM handover (HO), the gNB prepares one or more candidate cells and provides the candidate cell configurations to the UE through an RRC message. Then, the LTM cell switch is triggered by selecting one of the candidate configurations as the target configuration for the LTM by the gNB. The candidate cell configurations can only be added, modified, and released by the network via Radio Resource Control (RRC) signaling. As illustratively used herein, a cell refers to a geographical area covered by a frequency (or a frequency range) emitted by a base station in a cellular network.

[0060] It is realized that it would be desirable, from a security and / or signaling perspective, to enable alternative LTM handover procedures. Illustrative embodiments provide enhanced LTM handover procedures as will be illustratively described below in the context of FIGS. 5, 6, and 7. Prior to illustratively describing enhanced LTM handover procedures, existing key chaining and existing LTM handover procedures will be briefly described in the context of FIGS. 3 and 4, respectively.

[0061] FIG. 3 illustrates a key chaining procedure (procedure 300) in a communication network environment. As shown in procedure 300, whenever an initial access stratum (AS) security context needs to be established between a UE and a gNB, the AMF and the UE derive a KgNB and a Next Hop parameter (NH). The K8NB and the NH are derived from the AMF key KAMF. An NH Chaining Counter (NCC) parameter is associated with each K8NB and NH parameter. Every KgNB is associated with the NCC corresponding to the NH value from which it was derived.

[0062] As further shown in procedure 300, at initial setup, the K8NB is derived directly from KAMF, and is then considered to be associated with a virtual NH parameter with an NCC value equal to zero. Further, at initial setup, the derived NH value is associated with the NCC value one. At the UE, the NH derivation associated with NCC= I could be delayed until the first handover performing vertical key derivation. The decision by the AMF to send the K8NB key or the [NH, NCC] pair to the serving gNB is described in further detail in the above-referenced TS 33.501. The AMF does not send the NH value to gNB at the initial connection setup. The gNB initializes the NCC value to zero after receiving a Next Generation Application Protocol (NGAP) Initial Context Setup Request message. Since the AMF does not send the NH value to gNB at the initial connection setup, the NH value associated with the NCC value one cannot be used in the next Xn handover or the next intra-gNB handover, for the next Xn handover or the next intra-gNB -CU handover the horizontal key derivation will apply. Note that CU refers to Centralized Unit which provides support for the higher layers of the protocol stack such as, by way of example, SDAP (Service Data Adaption Protocol), PDCP (Packet Data Convergence Protocol) and RRC (Radio Resource Control) layers, while DU refers to Distributed Unit which provides support for the lower layers of the protocol stack such as RLC (Radio Link Control), MAC (Medium Access Control), and Physical layers. Note that, in some examples, an intra- gNB handover occurs between cells of the same gNB, while inter-gNB handover occurs between cells of different gNBs.

[0063] One of the rules specified for the AMF in the above-referenced TS 33.501 states that the AMF always computes a fresh [NH, NCC] pair that is given to the target gNB. An implication of this is that the first [NH, NCC] pair will never be used to derive a K8NB. It only serves as an initial value for the NH chain. The UE and the gNB use the K8NB to secure the communication between each other. On handovers and at transitions from RRC_INACTIVE to RRC_CONNECTED states, the basis for the K8NB that will be used between the UE and the target gNB, called KNG-RAN*, is derived from either the currently active K8NB or from the NH parameter. If KNG-RAN* is derived from the currently active K8NB, this is referred to as a horizontal key derivation, and if the KNG-RAN* is derived from the NH parameter, the derivation is referred to as a vertical key derivation. As NH parameters are only computable by the UE and the AMF, it is arranged so that NH parameters are provided to gNB from the AMF in such a way that forward security can be achieved. On handovers with vertical key derivation, the NH is further bound to the target PCI (Physical Cell Identifier) and its frequency ARFCN-DL (Absolute Radio-Frequency Channel Number for Down Link) before it is taken into use as the KgNB in the target gNB. On handovers with horizontal key derivation, the currently active K8NB is further bound to the target PCI and its frequency ARFCN-DL before it is taken into use as the KgNB in the target gNB.

[0064] Accordingly, in summary, for both horizontal and vertical key derivation, the PCI and the DL frequency are used. Horizontal key derivation makes use of the previous key. Vertical key derivation does a refresh through use of NH. The vertical key generation is used to separate key space of each RAN node. The NH value is provided to the RAN node by the AMF. The vertical keys generated by each RAN node use a fresh NH value provided by AMF. Thus, the security domain is detached from the previous RAN node. In short, for horizontal key derivation, the inputs are the current KgNB (current active key), PCI, and DL frequency, and the output is the K8NB. In vertical key derivation, the inputs are a fresh NH value (provided by the AMF to the serving RAN node after path switch), PCI, and DL frequency, and the output is the KgNB-

[0065] Given the key chaining procedure 300, FIG. 4 illustrates a typical LTM handover procedure 400 (procedure 400) including steps 1-38 and involving a UE 402, a gNB (source gNBl) 404, a gNB (target gNB) 406, and an AMF 408. Procedure 400, inter alia, describes the coordination of NCC between the network (AMF 408) and the UE 402. During the initial access, AMF 408 shares the security key and does not share NCC. The gNB 404 initializes the NCC to 0 and UE 402 also uses the NCC as 0. During the first inter-gNB handover, AMF 408 shares the NCC (incremented by 2).

[0066] Step 1: gNB 404 stores the NH key and NCC received from AMF 408 during path switch procedure of a handover execution phase.

[0067] Step 2: gNB 404 sends the measurement configurations through RRC reconfiguration to UE 402.

[0068] Step 3: UE 402 measures the neighbor cells and, upon meeting the measurement criteria, sends a measurement report to gNB 404.

[0069] Steps 4 and 5: gNB 404 makes a decision for an inter-gNB handover and sends a handover request message to gNB 406 (gNB2) including KNG-RAN* generated using the stored security information that includes NH and NCC and target cell information.

[0070] Steps 6-8: gNB 406 shares the NCC to UE 402 during handover preparation via RRC Reconfiguration (handover command).

[0071] Step 9: if NCC is same as previous, UE 402 executes a horizontal key update, else UE executes a vertical key update.

[0072] Steps 10 and 11: UE 402 performs a Random Access Channel (RACH) procedure with gNB 406 and sends the RRC Reconfiguration complete message to gNB 406.

[0073] Steps 12-17: gNB 406 performs a path switch procedure. During the path switch procedure, AMF 408 increases the NCC by 1 , generates the fresh NH, shares the NH and NCC through a path switch request acknowledgement, and stores the keys for the next handover. As the NCC has been increased by one, the next handover (either an intra-gNB handover or an inter-gNB handover) will use the vertical key update.

[0074] Steps 18-20: gNB 406 (now the serving gNB) makes a decision for an intra-gNB inter cell handover. gNB 406 initiates RRC reconfiguration for the handover and shares the new NCC which triggers the vertical key update procedure. Steps 21-23: Since UE 402 received the NCC increased by one, UE 402 performs the vertical key update, performs the RACH procedure with gNB 406, and sends RRC Reconfiguration Complete message to gNB 406.

[0075] Steps 24-30: UE 402 sends a measurement report and gNB 406 makes a decision of an inter-gNB handover with target gNB 404. gNB 406 sends a handover request to gNB 404 with KNG-RAN* generated by using the horizontal procedure since the NCC was used in the previous handover and no new NCC was received from AMF 408. gNB 404 includes the NCC in the handover command and sends to UE 402 via serving / source gNB 406.

[0076] Steps 31-33: Since the NCC is the same as the previous NCC, UE 402 executes the horizontal key update, performs the RACH procedure with gNB 404, and sends the RRC Reconfiguration complete message to gNB 404.

[0077] Steps 34-38: The procedures of step 12-16 are repeated.

[0078] Accordingly, as described above in procedure 400, the NCC value is indicated in the handover command by the target gNB for each cell change. The NCC value is used to decide whether UE 402 should implement horizontal / vertical key derivation. However, it would be desirable in an LTM switching context that the candidate cell configurations are re-used without a new RRC reconfiguration message. In case the same NCC value is used over and over again, only horizontal key derivation would be possible. Thus, procedure 400 is not aligned with the desired security paradigm as different gNBs need a fresh key with a new NH value.

[0079] Such a non-reconfiguration solution, for example, would provide both processing and overhead savings due to less signaling between components, as well as security enhancements in that less signaling between components would provide less opportunities for malicious actors to attempt to intercept signals or otherwise attack components in the communication network environment.

[0080] Illustrative embodiments provide the above and other technical solutions by providing enhanced procedures that utilize a new RRC message that carries security configurations (e.g., Master key Update IE) and an indication (e.g., intraGnbHOKeyChangelndicator) in the target cell configuration during LTM preparation.

[0081] During LTM candidate configuration preparation, the target LTM cell configuration may include the intraGnbHOKeyChangelndicator in the configuration. The serving CU shares the target configurations including security configurations (e.g., NCC, etc.) in a source configuration with the UE through an RRC reconfiguration procedure, or alternatively the serving CU can share the same through a new RRC message after the RRC reconfiguration procedure. Thereafter, the CU shares the security configurations (e.g., NCC, etc.) to the UE through a new RRC message after the path switch procedure. The UE stores the security information and uses the data during the LTM handover or failure recovery to a selected LTM candidate cell. Security configurations alternately can be MasterKeyUpdatelE.

[0082] The UE can use a legacy method to decide whether to use the vertical or horizontal key derivation method. The legacy method here is to consider the NCC value configured for a specific candidate cell: (i) if the same NCC value, then us a horizontal handover; (ii) if an incremented NCC value, then use a vertical handover; and (iii) if there has been no security update, then skip the key change.

[0083] In one illustrative embodiment, upon initiation of a path switch procedure, when the AMF shares the NCC and NH pair, the current serving CU generates new keys and shares them with LTM candidates through Xn signaling and shares the security configuration (e.g., MasterKeyUpdatelE including NCC, etc.) with the UE through the new RRC message. The UE stores the security configuration for further use during an LTM handover or recovery to an inter-gNB LTM cell. Note that, in the above-mentioned illustrative embodiment, there is no key change for intra-gNB cell change. The UE knows whether the cell-switch is between intra or inter-gNB based on the Group- ID included in the candidate configuration.

[0084] Further, the absence of the flag intraGnbHOKeyChangelndicator in the target configuration during the LTM handover preparation is considered as intraGnbHOKeyChangelndicatoi -false.

[0085] In a variation to the above-mentioned illustrative embodiment, when target gNB decides to include intraGnbHOKeyChangelndicator as true: (i) the UE generates vertical keys for an intra-gNB handover after an inter-gNB handover since the shared NCC is different compared to the current NCC stored at the UE; and (ii) if the UE performs a vertical key update for an intra-CU handover, a subsequent handover will be a horizontal key update and the serving gNB updates new keys to other candidates after the intra-CU handover.

[0086] In another illustrative embodiment, to address the security issue that the UE may re-use the key multiple times: (i) the UE is not allowed to trigger a cell change until a security update is done (Option 1 below); or (ii) the target DU is configured to not trigger cell change until the key configuration of the UE is updated (Option 2 below). FIG. 5 illustrates an enhanced LTM handover procedure (e.g., procedure 500) in a communication network environment according to an illustrative embodiment.

[0087] Procedure 500 involves a UE 502, a first gNB 504 with a DU 1 and a CU 1 , a second gNB 506 with a DU 2, a DU 2.2, and a CU 2, a third gNB 508 with a DU 3 and a CU 3, and an AMF 510. Procedure 500 corresponds to the above-mentioned embodiment wherein the absence of the flag intraGnbHOKeyChangelndicator in the target configuration during the LTM handover preparation is considered as intraGnbHOKcyChangelndicatoi-falsc, and security configurations are shared through a new RRC message or a source reconfiguration message.

[0088] Steps 1-3: UE 502 is registered, a Packet Data Unit (PDU) session setup occurs, and an LTM handover decision is made.

[0089] Steps 4-7: The source CU (CU 1) initiates the LTM candidate preparation with target cells. Target cells include intraGnbHOKeyChangelndicatoi -false or do not include intraGnbHOKeyChangelndicator in the LTM handover configuration.

[0090] Step 8: The source CU prepares the RRC reconfiguration including security configurations in the source configuration and including target configurations. Alternately, if the RRC reconfiguration does not contain the security configurations, then the same can also be shared to UE 502 through a new RRC signaling after the RRC reconfiguration procedure.

[0091] Steps 9 and 10: The RRC reconfiguration procedure is performed and contains security configuration information in the source configuration.

[0092] Steps 11-17: Inter-CU LTM handover execution is performed using a horizontal key derivation as it is a first inter-CU handover. In this case, UE 502 does not have any unused NCC value.

[0093] Steps 18-20: The path switch procedure is performed and AMF 510 shares a new NH and incremented NCC and CU 2 shares the new keys with all prepared LTM candidates.

[0094] Steps 21-23: the new source CU (CU 2) shares the new security configurations through the new RRC signaling procedures. MasterKeyUpdatelE can be reused here to share the new security configurations in the new RRC message.

[0095] Steps 24 and 25: UE 502 stores the new security configurations to use in a further handover.

[0096] Steps 26-31: UE 502 performs an intra-CU handover. Since the indication intraGnbHOKeyChangelndicator is false or the flag is absent in the target cell configuration, UE 502 performs no key update procedure. Further, the inter-CU handover performs the vertical key update procedure as NH and NCC are not used.

[0097] Step 32: The next inter-CU handover shall perform the vertical key update procedure.

[0098] As described above, UE 502 is configured with a flag intraCel 1 HOKcyGcncration=falsc in the source RRC configuration. The flag can be indicated per candidate cell. If intraCellHOKeyGeneration is false in the target cell configuration, then UE 502 does not generate any key (neither horizontal nor vertical) for the intra-CU handover cases.

[0099] Alternately, UE 502 may consider intraCellHOKeyGeneration^ false if the flag is missing in the target cell configuration.

[0100] After an intra-CU handover, when UE 502 performs an inter-CU handover, UE 502 performs a vertical key derivation as NCC and NH were not used in the intra-gNB handover.

[0101] FIG. 6 illustrates an enhanced LTM handover procedure (e.g., procedure 600) in a communication network environment according to another illustrative embodiment.

[0102] Procedure 600 involves a UE 602, a first gNB 604 with a DU 1 and a CU 1 , a second gNB 606 with a DU 2, a DU 2.2, and a CU 2, a third gNB 608 with a DU 3 and a CU 3, and an AMF 610. Procedure 600 corresponds to the above-mentioned embodiment wherein intraCellHOKeyGenerationlndication is set as true in the target cell configuration, and security configurations are shared through a new RRC message or a source reconfiguration message.

[0103] Steps 1-3: UE 602 is registered, a PDU session setup occurs, and an LTM handover decision is made.

[0104] Steps 4-7: The source CU (CU 1) initiates the LTM candidate preparation with target cells. Target cells include intraGnbHOKcyChangclndicatoi-truc in the LTM handover configuration.

[0105] Step 8: The source CU prepares the RRC reconfiguration including security configurations in the source configuration and including target configurations. Alternately, if the RRC reconfiguration does not contain the security configurations, then the same can also be shared to UE 602 through a new RRC signaling after the RRC reconfiguration procedure.

[0106] Steps 9 and 10: The RRC reconfiguration procedure is performed and contains security configuration information in the source configuration.

[0107] Steps 11-17: Inter-CU LTM handover execution is performed using a horizontal key derivation as it is a first inter-CU handover. In this case, UE 602 does not have any unused NCC value. Steps 18-20: The path switch procedure is performed and AMF 610 shares a new NH and incremented NCC and shares the new keys with all prepared LTM candidates.

[0108] Steps 21-23: the new source CU (CU 2) shares the new security configurations through the new RRC signaling procedures. MasterKeyUpdatelE can be reused here to share the new security configurations in the new RRC message.

[0109] Steps 24 and 25: UE 602 stores the new security configurations to use in a further handover.

[0110] Steps 26-31: UE 602 performs an intra-CU handover. Since the indication intraGnbHOKeyChangelndicator is true in the target cell configuration, UE 602 performs a vertical key update procedure as the NH and NCC are not used. Further handovers perform a horizontal key update procedure.

[0111] Step 32: The source CU shares the new horizontal keys with other LTM prepared candidates.

[0112] Steps 33-36: The source CU shares the same security configuration (same NCC) through the new RRC signaling and UE 602 considers the next handover to perform a horizontal key generation method. Alternately, since UE 602 performs a key update as intraCellHOKeyGenerationlndication is true for an intra-CU handover, UE 602 can consider no further security configuration update needed from the source CU for the next handover and UE 602 can safely do the next handover and use the horizontal key update method.

[0113] FIG. 7 illustrates an enhanced LTM handover procedure (e.g., procedure 700) in a communication network environment according to yet another illustrative embodiment.

[0114] Procedure 700 involves a UE 702, a first gNB 704 with a DU 1 and a CU 1, a second gNB 706 with a DU 2, a DU 2.2, and a CU 2, a third gNB 708 with a DU 3 and a CU 3, and an AMF 710. Procedure 700 corresponds to the above-mentioned embodiment wherein an LTM handover is not triggered until the key configuration of the UE is updated.

[0115] Steps 1-3: UE 702 is registered, a PDU session setup occurs, and an LTM handover decision is made, i.e., indicate horizontal key to target CUs.

[0116] Steps 4-7: The source CU (CU 1) initiates the LTM candidate preparation with target cells.

[0117] Step 8: The source CU prepares new security configurations in the source configuration. A flag indicates UE (702) behavior for key generation, alternatively an NCC value is configured. Steps 9 and 10: The RRC reconfiguration procedure is performed and contains the new security configuration information in the source configuration.

[0118] Steps 11-16: Inter-CU LTM handover execution is performed using a horizontal key derivation. UE 702 uses the new security configuration and deletes the security configuration thereafter.

[0119] Step 17: Access notification occurs from DU 2 to CU 2.

[0120] Step 18: LI measurement report is sent from UE 702 to DU 2.

[0121] Step 19: CU2 indicate to DU2 about the security config update at UE. DU 2 makes an LTM handover decision not to trigger cell change when security is not updated (Option 1).

[0122] Steps 20 and 21: DU 1 sends a cell switch command (originating from DU 2) to UE 702 and no cell change is triggered since no key configuration is available (Option 2).

[0123] Accordingly, in procedure 700, the target DU is configured not to trigger LTM cell change until key configuration of UE 702 is performed. The indication is sent by the source CU to DU. Alternately, UE 702 is not allowed to trigger a cell change until a security update is done. As shown in step 8 of procedure 700, CU 1 can consider indicating to UE 702 through an indication in the new RRC message / reconfiguration message to control the UE behavior to perform vertical / horizontal key generation.

[0124] It is to be appreciated that the particular processing operations and other system functionality described in conjunction with the diagrams described herein are presented by way of illustrative example only and should not be construed as limiting the scope of the disclosure in any way. Alternative embodiments can use other types of processing operations and messaging protocols. For example, the ordering of the steps may be varied in other embodiments, or certain steps may be performed at least in part concurrently with one another rather than serially. Also, one or more of the steps may be repeated periodically, or multiple instances of the methods can be performed in parallel with one another.

[0125] It should again be emphasized that the various embodiments described herein are presented by way of illustrative example only and should not be construed as limiting the scope of the claims. For example, alternative embodiments can utilize different communication system configurations, user equipment configurations, base station configurations, authorization processes, messaging protocols and message formats than those described above in the context of the illustrative embodiments. These and numerous other alternative embodiments within the scope of the appended claims will be readily apparent to those skilled in the art.

Claims

Claims:

1. An apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to: receive a radio resource control message from a radio access node with which the apparatus is connected, the radio resource control message comprising handover-enabling data to enable the apparatus to perform multiple handover operations in response to the radio resource control message.

2. The apparatus of claim 1, wherein the handover-enabling data comprises security configurations to enable the apparatus to perform multiple handover operations in response to the radio resource control message.

3. The apparatus of claim 2, wherein the security configurations comprise key derivation parameters for performing one or more key derivation procedures.

4. The apparatus of claim 1 , wherein the handover-enabling data comprises a master key update information element.

5. The apparatus of claim 1, wherein the handover-enabling data comprises an intraradio access node handover key change indicator settable by one or more target radio access nodes.

6. The apparatus of claim 5, wherein, when the intra-radio access node handover key change indicator is set to a first value, the apparatus performs a key change for an intra-radio access node handover for a corresponding target radio access node.

7. The apparatus of claim 6, wherein, when the intra-radio access node handover key change indicator is set to a second value, the apparatus does not perform a key change for an intra-radio access node handover for a corresponding target radio access node.

8. The apparatus of claim 1, wherein the handover-enabling data comprises an indication that the apparatus is not allowed to perform a handover operation until a security update is performed.

9. The apparatus of claim 1, wherein the multiple handover operations are lower layer- triggered mobility (LTM) handover operations.

10. A method comprising: receiving, at user equipment, a radio resource control message from a radio access node with which the user equipment is connected, the radio resource control message comprising handover-enabling data to enable the user equipment to perform multiple handover operations in response to the radio resource control message; and utilizing, by the user equipment, the handover-enabling data to perform the multiple handover operations.

11. An apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to: generate a radio resource control message comprising handover-enabling data to enable user equipment to perform multiple handover operations in response to the radio resource control message; and send the radio resource control message to the user equipment.

12. The apparatus of claim 11, wherein the handover-enabling data comprises security configurations to enable the user equipment to perform multiple handover operations in response to the radio resource control message.

13. The apparatus of claim 12, wherein the security configurations comprise key derivation parameters for performing one or more key derivation procedures.

14. The apparatus of claim 11, wherein the handover-enabling data comprises a master key update information element.

15. The apparatus of claim 11, wherein the handover-enabling data comprises an intraradio access node handover key change indicator settable by one or more target radio access nodes.

16. The apparatus of claim 15, wherein, when the intra-radio access node handover key change indicator is set to a first value, the user equipment is instructed to perform a key change for an intra-radio access node handover for a corresponding target radio access node.

17. The apparatus of claim 16, wherein, when the intra-radio access node handover key change indicator is set to a second value, the user equipment is instructed not to perform a key change for an intra-radio access node handover for a corresponding target radio access node.

18. The apparatus of claim 11, wherein the handover-enabling data comprises an indication that the user equipment is not allowed to perform a handover operation until a security update is performed.

19. The apparatus of claim 11, wherein the multiple handover operations are lower layer-triggered mobility (LTM) handover operations.

20. A method comprising: generating, at a radio access node, a radio resource control message comprising handover-enabling data to enable user equipment to perform multiple handover operations in response to the radio resource control message; and sending, from the radio access node, the radio resource control message to the user equipment.

21. The method of claim 20, wherein the radio access node is configured not to trigger a cell change until a key configuration of the user equipment is performed.

22. The method of claim 20, wherein the user equipment is not allowed to trigger a cell change until a security update is performed.

23. The method of claim 20, wherein the radio access node indicates to the user equipment in the radio resource control message to perform one of a vertical key generation and a horizontal key generation.

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